Anti-static sound-recording medium and method of making the same



United States Patent Ofiicc 2,710,402 Patented June 7, 1955 ANTI-STATICSOUND-RECORDING MEDIUM AND METHOD OF MAKING THE SAME Richard G. Rowe,Redding Ridge, Conn., assignor to Dictaphone Corporation, Bridgeport,Conn., a corporation of New York No Drawing. Original application May11, 1950, Serial No. 161,473. Divided and this application August 11,1952, Serial No. 303,833

4 Claims. (Cl. 106-37) This invention relates to a novel anti-staticagent adapted to be incorporated in a sound-recording medium to reducethe tendency of'static electrical charges to accumulate on the surfacesof such a medium, and more particularly to sound-recording mediaincorporating such an anti-static agent and a method of makingsuchmedia. The anti-static agent of the present invention is particularlyuseful for reducing the accumulation of static charges on the well-knownwax recording cylinders, and will be illustratively described. in thatenvironment. The phrase sound-recording wax will be used hereafter todesignate the material of which such cylinders are made, although as iswell known sound-recording waxes are ordinarily largely composed ofmetallic soaps, higher fatty acids, or both, and may contain no wax atall in a strict chemical sense. i i

The present application is a division of my pending application SerialNo. l 6l,473 filed May 11, 1950, now abandoned. The claims of thepresent case are directed to sound recording media incorporatinganti-static agents such as those claimed in'my co-pending case, and to 1methods of making such media.

For many years sound-recording wax cylinders have been used for avariety of sound-recording purposes. As ordinarily used, such cylindersare mounted on a horizontal rotating mandrel of a dictating machine, anda laterally movable sound-responsive stylus cooperates with the rotatingcylinder to cut a helical sound track in the surface thereof. As anincident of this cutting action short, curly fibers of the wax materialare removed from the surface of the cylinder, which fibers are sometimes1 referred to as chips, and a container or chip collector is usuallyprovided beneath the cylinder to collect those chips that fall oh. thecylinder. It is, of course, desirable that all of the chips fall off thecylinder as soon as they have been formed so that they may be collectedand disposed of in an orderly manner, but unfortunately there is atendency under normal circumstances for the majority of the chips formedto continue to adhere to the cylinder surface. Although the reasons forthe adherence of the chips to the surface of the cylinder are notcompletely understood, my investigations indicate that the principalreason for this undesired adherence of the chips is the accumulation ofa static electrical charge on the surface of the cylinder.

The removal of the chips from the surface of the cylinder is desirablefor a variety of reasons. The cylinders are usually kept in cylindricalcontainers having an interior lining made of a fibrous fabric, and ifthe chips are not completely removed from the cylinder surface, they maybe transferred to the interior of the container. Continued use of acontainer that has been contaminated with chips may cause the soundrecord to be scratched or otherwise deformed as the cylinder is insertedinto or withdrawn from the container. If the chips are not removed bycontact with the interior of the container, they may interfere withtranscription of the sound record. Moreover, the adhering chips aregenerally untidy since, if they do not fall into the chip collector ofthe dictating machine for disposal in a controlled manner, they have atendency to fly off in the atmosphere and adhere to clothing, carpetsand the like.

It is accordingly an object of the present invention to provide a waxsound-recording medium in cylindrical or other form that is of such acharacter that chips cut from the surface thereof by a sound-responsivestylus do not tend to adhere to the surface of the medium. It is anotherobject of the invention to provide a novel antistatic agent adapted tobe incorporated in a sound-recording wax to reduce the tendency ofstatic electrical charges to accumulate on the surface of the soundrecord. It is a further object of the invention to provide asoundrecording wax incorporating such an anti-static agent. It is stillanother object of the invention to provide a method of making such ananti-static agent and a method of incorporating it effectively into asound-recording medium. Other objects of the invention will be in partobvious and in part pointed out hereafter.

The objects of the present invention may be achieved in general byproviding a sound-recording wax contain ing a relatively small quantityof tri-(n-butylamine) phosphate. I have found that the tendency ofstatic electrical charges to collect on the surface of a sound-recordingwax containing a small proportion of tri-(n-butylamine) phosphate ismaterially reduced, and that when this compound is incorporated in thewax nearly all of the chips formed by the action of a sound-responsivestylus thereon fall off as soon as they are formed. The quantity of thetri-(n-butylamine) phosphate incorporated in the soundrecording wax mayvary from 2% to by weight, although in most cases preferred results areobtained by using about 4% by weight of the phosphate.

The present anti-static agent is preferably added to the wax while thewax is in molten condition and prior to the time that it is cast into acylinder. So far as I am aware, tri-(n-butylamine) phosphate is a newcompound.

In order to point out more fully the nature of the present invention,the following illustrative procedure is given for makingtri-(n-butylamine) phosphate and also for incorporating it in asound-recording wax to produce a sound-recording medium havinganti-static properties: A stainless steel vessel equipped with a motordriven agitator and cooling coils is charged with 219 lbs. ofn-butylamine dissolved in gallons of methanol. To this solution 116.7lbs. of orthophosphoric acid is added slowly with stirring. Duringaddition of the phosphoric acid a suitable refrigerant is passed throughthe coils of the reaction vessel to maintain the reaction temperature atabout 10 C. The reaction proceeds readily and practicallyinstantaneously and the tri-(n-butyl amine) phosphate is formed as awhite precipitate. When addition of the phosphoric acid is complete, therefrigerant is cut off to permit the reaction mixture to warm up to roomtemperature and stirring continued for about an hour to ensurecompleteness of reaction.

The tri-(n-butylamine) phosphate thus formed is separated by filtrationfrom other components of the mixture and purified by repeated washingswith acetone, after which it is filtered and air dried. The purifiedpowdered product fuses at about 165 C. It is soluble to the extent ofabout 25 parts per 100 in water at room temperature and to the extent ofabout 10 parts per 100 in ethanol at C. Its specific conductivityalthough not comparable with that of a metal, is substantially higherthan the conductivity of other chemically related materials.

The tri-(n-butylamine) phosphate as thus formed may be incorporated in aconventional sound-recording wax,

for example, the wax formula disclosed at page 35 of The Reproduction ofSound by Henry Seymour (1918) in the following manner: A suitably heatedvessel is charged with 3,333 lbs. of S. Stearine (commercial stearicacid) and the S. Stearine is melted. To the molten S. Stearine asolution of 208 lbs. of 98% caustic soda in 525 lbs. of water is slowlyadded. As the caustic soda solution is added, neutralization of the S.Stearine occurs and the mixture is heated to such an extent as to removeall water from the resulting soap mixture.

After completion of this neutralization step, 178 lbs. of red lead isadded to the mixture in the reaction vessel. The addition of the redlead may be effected by removing a small quantity of the molten soapmixture from the heated vessel and mixing the red lead in powder formtherewith, after which the mixture of red lead and soap is added to andmixed with the main body of material in the vessel.

When the red lead has been incorporated into the molten soap, 212.5 lbs.of trHn-butylamine) phosphate, 950 lbs. of parafiin wax, and 119.5 lbs.of myrtle wax are successively added to the mixture in the kettle, andheating of the mixture continued at about 375 F. for a period of about24 hours.

At the end of the heating period the molten mixture is cast intocylinders in the usual manner, and the cylinders machined to form thedesired sound-recording surface.

Cylinders made in accordance with the foregoing procedure are strikinglysuperior to conventional cylinders in respect to the extent to whichchips fall off the surfaces thereof when they are cut by asound-responsive stylus. Moreover, tests have shown that the electricalconductivity of the wax is appreciably increased by incorporation of thepresent anti-static agent therein.

It is, of course, to be understood that the foregoing detailed procedureis illustrative only and that numerous changes may be made thereinwithout departing from the scope of the invention. Many different waxformulae have been previously proposed for sound-recording purposes andmy experiments indicate that the present antistatic agent can be used inany of these known formulae to improve the anti-static properties of theresulting soundrecording wax. Since many embodiments might be made ofthe persent invention and since many changes might be made in theembodiment disclosed herein, it is to be understood that the foregoingdescription is to be interpreted as illustrative only and not in alimiting sense.

What I claim is: 1. A sound-recording medium having anti-static prop- 1erties, said medium comprising a sound-recording wax containing from 2%to 10% by weight of tri-(n-butylamine) phosphate.

2. A sound-recording medium having anti-static prop erties, said mediumcomprising a sound-recording wax containing about 4% by weight oftri-(n-butylamine) phosphate.

3. The method of making a sound-recording medium having anti-staticproperties which comprises preparing a melt of a sound-recording wax,mixing with said molten wax between 2% and 10% by weight oftri-(n-butylamine) phosphate and cooling and casting the resultingmixture to form a solid sound-recording medium.

4. The method of making a sound-recording medium having anti-staticproperties which comprises heating a mixture of fatty acid, causticalkali, and parafiin wax to form a moltenmass, adding to said moltenmass from about 2% to 10% by weight of tri-(n-butylamine) phosphate andcooling and casting the resulting mixture to form a solidsound-recording medium.

No references cited.

1. A SOUND-RECORDING MEDIUM HAVING ANTI-STATIC PROPERTIES, SAID MEDIUMCOMPRISING A SUND-RECORDING WAX CONTAINING FROM 2% TO 10% BY WEIGHT OFTRI-(N-BUTYLAMINE) PHOSPHATE.